During small incision surgery, and particularly during ophthalmic surgery, small probes are inserted into the operative site to cut, remove or otherwise manipulate tissue. During these surgical procedures, the surgical site typically is flushed with an irrigating solution and the irrigating solution and tissue is aspirated from the surgical site. The types of aspiration system used, prior to the present invention, where generally characterized as either flow controlled or vacuum controlled, depending upon the type of pump used in the system, and each type of system has certain advantages.
Vacuum controlled aspiration systems are operated by setting a desired vacuum level, which the system seeks to maintain. Flow rate information is not available directly. Vacuum controlled aspiration systems typically use a venturi or diaphragm pump. Vacuum controlled aspiration systems offer the advantages of quick response times, control of decreasing vacuum levels and good fluidic performance while aspirating air, such as during an air/fluid exchange procedure.
Disadvantages of such systems are the lack of flow information resulting in high flows during phacoemulsification/fragmentation coupled with a lack of occlusion detection. Vacuum controlled systems are difficult to operate in a flow controlled mode because of the problem of non-invasively measuring flow in real time.
Flow controlled aspiration systems are operated by setting a desired aspiration flow rate for the system to maintain. Flow controlled aspiration systems typically use a peristaltic, scroll or vane pump. Flow controlled aspiration systems offer the advantages of stable flow rates and automatically increasing vacuum levels under occlusion. Disadvantages of such systems are relatively slow response times, undesired occlusion break responses when large compliance components are used and vacuum can not be linearly decreased during tip occlusion. In addition, peristaltic pumps produce pulsations in the aspiration fluid flow. When such pumps are in fluid communication with a surgical site, these pump pulsations can be manifested at the surgical site. Flow controlled systems are difficult to operate in a vacuum controlled mode because time delays in measuring vacuum can cause instability in the control loop, reducing dynamic performance.
One surgical system currently commercially available, the Millennium from Storz Instrument Company, contains both a vacuum controlled aspiration system (using a venturi pump) and a flow controlled aspiration system (using a scroll pump). The two pumps can not be used simultaneously, and each pump requires separate aspiration tubing and cassette.
Another currently available system, the ACCURUS® system from Alcon Laboratories, Inc., contains both a venturi pump and a peristaltic pump that operate in series. The venturi pump aspirates material from the surgical site to a small collection chamber. The peristaltic pump pumps the aspirate from the small collection chamber to a larger collection bag. The peristaltic pump does not provide aspiration vacuum to the surgical site. Thus, the system operates as a vacuum controlled system.
Accordingly, a need continues to exist for a surgical system that operates in both vacuum controlled and flow controlled modes.